LOCKING CHESTS AND DOORS
About Locking Chests and Doors:
If you place a sign on a chest or a door without shift-clicking, it will make the chest or door private. The sign should look similar to the captioned picture to the right.
To allow multiple users access to the chest, repeat the above process to place a second sign on the door or chest you want to share access to. Now type this command
/blocklocker <line number> <playername>
You must specify the line number (a number between 2-4) which corresponds to the line number on the sign. If you want more users you can place extra signs on the chest and repeat this command!